Note: 200590.1 - bde_session_locks.sql - Locks for given Session ID (8.1-9.2)
Note: 15476.1 - FAQ about Detecting and Resolving Locking Conflicts
Note: 198150.1 - How To Indentify The Row Which is Locked By an Other User's Session
Script: To display Locks and give the SID and Serial# of the Session to Kill). [ID 1020007.6 ]

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Every one telling blocking session. Blocking session and locking and both are same?.
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Yes, pretty much. Locking session should be blocking the other session that's interested in the same row or segment. Depending upon the situation (whether it's row level lock or table lock exclusive), the blocking session is locking session and the blocked session is locked session. It could even be on buffer cache or shared pool too (different terminology for those (b)locks.